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Two-dimensional (2D) transition metal dichalcogenides (TMDs) are considered to be promising building blocks for the next generation electronic and optoelectronic devices. Various doping schemes and work function engineering techniques have been explored to overcome the intrinsic performance limits of 2D TMDs. However, a reliable and long-time air stable doping scheme is still lacking in this field. In this work, we utilize keV ion beams of H2+ to irradiate layered WSe2 crystals and obtain efficient n-type doping effect for all irradiated crystals within a fluence of 1 × 1014 protons·cm−2 (1e14). Moreover, the irradiated WSe2 remains an n-type semiconductor even after it is exposed to ambient conditions for a year. Localized ion irradiation with a focused beam can directly pattern on the sample to make high performance homogenous p-n junction diodes. Raman and photoluminescence (PL) spectra demonstrate that the WSe2 crystal lattice stays intact after irradiation within 1e14. We attribute the reliable electron-doping to the significant increase in Se vacancies after the proton irradiation, which is confirmed by our scanning transmission electron microscope (STEM) results. Our work demonstrates a reliable and long-term air stable n-type doping scheme to realize high-performance electronic TMD devices, which is also suitable for further integration with other 2D devices. [ABSTRACT FROM AUTHOR]

Monolayer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) have attracted much attention for use in electronic and optical applications. Due to their sensitivity to gases, the surface of these materials has been protected by coating with polymers such as polyethyleneimine (PEI). However, the effects of such coating layers on the electronic and optical properties of MX2 are not well understood. In this work, density functional theory calculations are used to study the effects of adsorption of PEI on monolayer MX2 substrates based on the electronic and optical properties before and after PEI adsorption. The results show that the bandgap of the substrate decreases significantly upon PEI adsorption, while the optical spectra show only slight modification with a decrease of intensity at short wavelengths around 300 nm. The results also indicate that PEI adsorption results in n-type doping states in MX2 but does not deteriorate the optical properties in the visible range. [ABSTRACT FROM AUTHOR]

Epitaxial growth of n-type semiconductor diamond films on (111)-oriented diamond has been achieved by hot-filament chemical vapor deposition (HFCVD) using a methane source and a trimethylphosphine dopant source. Secondary-ion mass spectrometry showed that the phosphorus atoms are incorporated into the films in the concentration range of 1018–1019 cm−3 from the vapor phase. Hall-effect measurements confirmed n-type conductivity in a wide temperature range up to 873 K. Electrons are thermally activated from a phosphorus donor level of approximately 0.57 eV as dominant carriers under the presence of tungsten atoms with concentrations of around 1018 cm−3 from filaments. These results indicate that HFCVD has the potential to be applied to an n-type doping process for fabricating diamond electronic devices in the phosphorus concentration range of not lower than 1018 cm−3. [ABSTRACT FROM AUTHOR]

To facilitate potential applications of tungsten diselenide (WSe2) in electronics, controllable doping is of great importance. As an industrially compatible technology, plasma treatment has been used to dope two-dimensional (2D) materials. However, owing to the strong etching effect in transition metal dichalcogenides (TMDCs), it is difficult to controllably dope 2D WSe2 crystals by plasma. Herein, we develop a moderate ammonia plasma treatment method to prepare nitrogen-doped WSe2 with controlled nitrogen content. Interestingly, Raman, photoluminescence, X-ray photoelectron spectroscopy, and electrical measurements reveal abnormal n-doping behavior of nitrogen-doped WSe2, which is attributed to selenium anion vacancy introduced by hydrogen species in ammonia plasma. Nitrogen-doped WSe2 with abnormal n-doping behavior has potential applications in future TMDCs-based electronics. [ABSTRACT FROM AUTHOR]

Divalent IIA metals such as Be, Mg, Ca, Sr, Ba and transition IIB metals such as Zn, Cd were investigated as possible n-type dopants into the CuO theoretically by using the first-principles calculations based on density functional theory. By systematical analyses of the lattice parameters, the bond length, the electronic structure, the local density of states and the defect formation energy for various doping systems, it is revealed that Ca, Sr, Ba and Be are more suited for n-type doping into CuO as shallow donors, compared to Mg which introduces a relatively deep donor level in CuO. Meanwhile, Zn and Cd can hardly be doped into CuO due to the positive formation energy of relevant defects. [ABSTRACT FROM AUTHOR]

We have conducted a study of the electrical and photoluminescence properties of ZnSe films grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) (250 Torr, 400°C) with ethyl iodide and hydrogen chloride as n-type dopant sources. A higher peak electron concentration and a lower minimum resistivity were observed using hydrogen chloride (5.4 × 1018 cm−3, and .0070 ohm-cm, respectively), as opposed to ethyl iodide (1.55 × 1017 cm −3, and 0.067 ohm-cm, respectively). We show that the higher electron concentrations observed in the chlorine doped layers are due to a higher incorporation of chlorine atoms than that of iodine atoms, and that this may be a result of the different tetrahedral misfit factors for these atoms. Our photoluminescence and 77K Hall effect data support this conclusion. Growth rate depression was observed to be more severe for iodine doped layers than for chlorine doped layers. Thus, it appears that hydrogen chloride is a superior dopant source for low-temperature photoassisted MOVPE ZnSe growth of n-type layers for blue-green laser diodes in the pressure-temperature regime investigated. [ABSTRACT FROM AUTHOR]

The influence of cadmium doping in enhancing: (i) near-band edge (NBE) to deep-level emissions (DLE) photoluminescence intensity ratio, and (ii) chlorine incorporation in HCl doped ZnSe films, has been studied. The epitaxial ZnSe was grown using low-temperature photo-assisted organometallic vapor phase epitaxy (OMVPE) using DMSe, DMZn, and DMCd alkyl sources. More intense near band-edge emission is observed when the growth temperature is reduced from 400 to 360°C. The deep-level emissions show a threshold-like dependence on UV light intensity for a given temperature. Cadmium doping is found to improve the NBE/DLE photoluminescence intensity ratio, and this improvement is more pronounced at higher growth temperature. Properties of n-type ZnSe films codoped with cadmium and chlorine, using HCl and DMCd as dopant sources have also been investigated. Samples co-doped with Cd showed higher electron concentrations and this effect was more pronounced at lower UV intensities. By the use of Cd co-doping, we have achieved the highest electron concentrations (2.4 x 10 cm) yet reported for HCl doping of OMVPE-grown ZnSe. [ABSTRACT FROM AUTHOR]

We report the results of the transport properties and the recombination mechanisms of indium-doped HgCdTe(211)B (x ≈ 23.0% ± 2.0%) layers grown by molecular beam epitaxy. We have investigated the origin(s) of the background doping limitation in these layers. Molecular beam epitaxially grown layers exhibit excellent Hall characteristics down to indium levels of 2 x 10 cm. Electron mobilities ranging from (2-3) x 10 cm/v-s at 23K were obtained. Measured lifetime data fits very well with the intrinsic band-to-band recombinations. However, below 2 x 10 cm doping levels, mobility vs temperature curves starts to reflect nonuniformity in carrier distribution. Also, when we reduced the Hg vacancy concentration down to 10 cm range, by annealing at 150°C, Hall characteristics shows an increase in the nonuniformity in the epilayers. It was found that after annealed at 150°C, the obtained SR defect level has a different origin than the previously obtain Hg-vacancy related defect level. [ABSTRACT FROM AUTHOR]

A new indium precursor, triisopropyl indium (TIPIn), has been used for doping MCT at low carrier concentrations. Previous attempts using indium organometallics resulted in a strong memory effect where residual doping would persist for many growth runs. Introducing TIPIn on the tellurium inject line resulted in a similarly strong memory doping but this was not observed when feeding the dopant in on the cadmium injection line. The TIPIn is believed to have been forming a low volatility adduct with diisopropyl tellurium (DIPTe) in the feed line and to have continued to evaporate at a low but significant rate. By keeping the TIPIn and DIPTe precursors separate until they entered the reactor, the desired low 10 cm carrier concentration and flat indium profiles could be achieved with good reproducibility. Good electrical characteristics were measured for these layers with Auger limited lifetime >1 μs at 77K. [ABSTRACT FROM AUTHOR]